It is usual practice to provide layered evaporators for use in motor vehicle air conditioners by fabricating a refrigerant circuit with use of at least two kinds of formed metal plates.
For example, two kinds of formed plates used for conventional layered evaporators are intermediate plates having a refrigerant channel recess and upper and lower header recesses greater than the channel recess in depth and each provided with a refrigerant hole formed in the bottom wall of the header recess, and a partition intermediate plate having a refrigerant channel recess and upper and lower header recesses which have a greater depth than the channel recess and one of which has a refrigerant hole formed in its bottom wall, the bottom wall of the other header recess having no hole and serving as a partition. Each of pairs of adjacent intermediate plates having refrigerant holes are fitted to each other in juxtaposed layers with the recessed sides thereof opposed to each other to provide flat tube portions arranged in parallel, and upper and lower headers in communication with the flat tube portions. At an intermediate portion of the evaporator with respect to the direction of juxtaposition of the plates, the intermediate plate having the partition in the header recess is used as one of the intermediate plates for providing the flat tube portion, whereby the core of the heat exchanger is divided into a plurality of pass units (groups of flat tube portions, hereinafter referred to as “passes”). The refrigerant flows through the entire heat exchanger core in a U-shaped pattern or zigzag through a refrigerant circuit having at least one turn.
When the evaporator comprises at least two kinds of formed plates like the conventional layered evaporator, there is a need to use at least two kinds of plate forming dies. The formed intermediate plate having a conventional partition has a cuplike portion (header recess) which greatly differs from like portions of the other intermediate plate, hence the need for a specific die and an increased die cost. Another problem is also encountered in that an increase in the number of components makes the heat exchanger core complex to assemble and difficult to fabricate by an automated process.
With the conventional layered evaporator, the heat exchanger core is divided into a plurality of passes by the intermediate plate having a partition, while the core is adapted to permit the refrigerant to flow uniformly through the tubes therein (flat tube portions) to achieve a higher efficiency. In actuality, however, it is difficult to intentionally control the flow of refrigerant when the fluid flows from one pass to the next pass, and there arises the problem that an uneven flow is likely to occur within the pass.